The invention relates to an integrated circuit for generating a current which produces a voltage drop across a reference resistor, which voltage drop is determined by an input voltage. Such a circuit is generally referred to as a voltage-current converter.
In an integrated circuit the accuracy of a voltage-current conversion across a reference resistor of predetermined value depends on the spread of this reference resistor. The spread of this resistor mainly depends on the resistance per unit area of the layer of material forming the resistor and on the spread in width of the resistance track.
In a monolithic integrated semiconductor circuit, the resistance per unit area depends on the quotient of the specific resistance of the doped zone forming the resistor and the thickness of this doped zone. The spread in width of the resistance track depends on the tolerances of the process which determines the structure of the doped zone (photolithography, etching). Therefore, it was found to be impossible to effect a voltage-current conversion with a small spread by means of an integrated circuit.